Caption: Tangent wave. Diagram illustrating the relationship between the rotation of a circle and the corresponding tangent waves. As the circle spins, its extended diameter traces out a discontinuous tangent (or tan) graph. The tangent wave, along with the cosine and sine waves (see image C028/9393) are together known as the circular or trigonometric functions. They are of critical importance in mathematics for the analysis and modelling of periodic phenomena.